3 (3)Arrays and Strings for 11,12,college.pptx

nice ppt

1. Arrays and Strings

2. Arrays in C++ An array is defined as collection of elements of same type, stored in contiguous memory locations . Advantage of Arrays They make accessing elements easier by providing random access Sorting and searching operations are easy on arrays.

3. Arrays in C++ Accessing array elements An individual element within an array is accessed by use of an index. An index describes the position of an element within an array. Note : In C++ the first element has the index zero

4. Arrays in C++ One dimensional Arrays A one-dimensional array is a list of related variables. The general form of a one-dimensional array declaration is : datatype variable_name [size ]; datatype : base type of the array, determines the data type of each element in the array size : how many elements the array will hold variable_name : the name of the array #include < iostream > using namespace std ; int main () { int array[] = {5, 6, 2, 3 }; int size = sizeof (array)/ sizeof (array[0 ]); int k=0, reverse[size]; for( int i =size-1; i >= 0;i--) { reverse[k++] = array[ i ]; } for( int i =0; i <size; i ++) { cout << reverse[ i ] <<" "; } return 0; } Output : 3 2 6 5

5. Arrays in C++ Two dimensional Arrays The simplest form of a multidimensional array is the two-dimensional array. Here , we have a row index and a column index. Both the row's and column's index begins from Syntax: data_type variable_name [N][M] data_type is the type of array, like int , float, char, etc. variable_name is the name of the array. N is the number of rows. M is the number of columns.

6. Arrays in C++ #include < iostream > using namespace std ; int main() { int r1 = 2, c1 = 3; int r2 = 3, c2 = 2; int m1[r1][c1] = {{1, 2, 3}, {1, 1, 1 }}; int m2[r2][c2] = {{1, 2}, {1, 3}, {1, 1}}; if(c1 != r2 ) { cout << "Matrix multiplaction Not ";} else { int res[r1][c2]; for( int i =0; i <r1; i ++){ for( int j=0; j<c2; j++ ){ int sum =0; for( int k=0; k<r2; k++){ sum += (m1[ i ][k] * m2[k][j]); } res[ i ][j] = sum; } } //output the resultant matrix cout << "Resultant Matrix: \n"; for( int i =0; i <r1; i ++){ for( int j=0; j<c2; j++ ){ cout << res[ i ][j] << "\t"; } cout << "\n"; } } return 0; }

7. Strings in C++ A String is called as group of characters enclosed in double quotes. String creations in C++ C-style strings(The one-dimensional character array is used to store a string). Using string class C-style string creation A string is defined as a character array terminated by a null symbol ( ‘\0’ ). Syntax: char variablename [size]; Example: char s[20];

8. C-style Strings in C++ Example: Reading input using cin Problem: Entering the string “This is a test”, the above program only returns “This”, not the entire sentence . Reason: The C++ input/output system stops reading a string when the first whitespace character is encountered. Solution : Use another C++ library function, gets(). #include < iostream > int main() { char str [80]; cout << “Enter a string: “; cin >> str ; // read string from keyboard cout << “Here is your string: “; cout << str ; return(0 ); } #include < iostream > int main() { char str [80]; // long enough for user input? cout << “Enter a string: “; gets( str ); // read a string from the keyboard cout << “Here is your string: “; cout << str << endl ; return(0 ); }

9. C-style Strings in C++ C++ Library Functions for Strings: The most common are: strlen () : length of a string strcpy () : copy characters from one string to another strcat () : concatenation of strings strcmp () : comparison of strings String Length using function: #include < iostream > # include < cstring > int main() { char str [80]; cout << “Enter a string: “; gets( str ); cout << “Length is: “ << strlen ( str ); return(0);} String Length without using function: # include< iostream > using namespace std ; int main() { char s[20]; cin >>s; int len =0; for( int i =0;s[ i ]!='\0';i++) { len ++; } cout <<" Length: "<< len ; }

10. C-style Strings in C++ C++ Library Functions for Strings: The most common are: strcpy () : copy characters from one string to another strcat () : concatenation of strings strlen () : length of a string strcmp () : comparison of strings String Copy using function: #include < iostream > #include < cstring > int main() { char a[10]; strcpy (a, “hello”); cout << a; return(0); } String Copy without using function: # include< iostream > using namespace std ; int main() { char s[20],s1[20]; cin >>s; int i ; for( i =0;s[ i ]!='\0';i++) { s1[ i ]=s[ i ]; } s1[ i ]='\0'; cout <<s1; }

11. C-style Strings in C++ C++ Library Functions for Strings: The most common are: strcpy () : copy characters from one string to another strcat () : concatenation of strings strlen () : length of a string strcmp () : comparison of strings String Concatenation using function: #include < iostream > #include < cstring > int main() { char s1[21], s2[11]; cin >>s1>>s2; strcat (s1, s2); cout << s1 << endl << s2; } String Concatenation without using function: # include< iostream > #include< cstring > using namespace std ; int main() { char s1[20],s2[20]; cin >>s1>>s2; int l1= strlen (s1); int l2= strlen (s2); int i ; for( i =0;s2[ i ]!='\0';i++) { s1[l1++]=s2[ i ]; } s1[l1]='\0';

12. C-style Strings in C++ strcmp () - Comparison of Strings: The most common are: str_1 == str_2 : 0 str_1 > str_2 : positive number str_1 < str_2 : negative number strncmp (s1,s2,n)  function to compares the first  n  number of characters between the strings strlwr () function : This function is used to convert all the characters in a string to  lower case letters strupr () function : This function is used to convert all the characters in a string to  lower case letters //string comparison using function # include < iostream > #include < cstring > int main() { char str [60 ]; cout << “Enter password: “; gets( str ); if( strcmp ( str , “ welcome@skcet ”)) { cout << “Invalid password.\n ”; } else { cout << “Logged on.\n ”; } return(0); } //string comparison without using function # include< iostream > #include< cstring > using namespace std ; int main() { char s1[20],s2[20]; cin >>s1>>s2; int l1= strlen (s1); int l2= strlen (s2); int f=0; if(l1==l2) { for( int i =0;s1[ i ]!='\0';i++) { if(s1[ i ]==s2[ i ]) { f++; } else { break; } } } if(f==l2) { cout <<"Equal"; } else { cout <<"Not equal"; } }

13. C-style Strings in C++ strchr () function : Find a character in a String and return remaining string after it . strstr () function : The strstr () function in C++ finds the first occurrence of a substring in a string . If the substring is found, returns the pointer to the first character of the substring . If the substring is not found, a null pointer is returned. #include< iostream > #include< cstring > using namespace std ; int main() { char s1[20],k; cin >>s1>>k; char *p= strchr (s1,k); cout <<p; } #include< iostream > #include< cstring > using namespace std ; int main() { char s1[20],s2[20]; cin >>s1>>s2; char *p= strstr (s1,s2); if(p) { cout <<"Present"; } else { cout <<"Not present"; } }

14. C-style Strings in C++ strrev () function : This function reverse the given string. #include< iostream > #include< cstring > using namespace std ; int main() { char s1[20]; cin >>s1; strrev (s1); cout << endl <<s1; }

15. Strings class in C++ String using string class: The string class stores the characters as a sequence of bytes with the functionality of allowing access to the single-byte character In the case of strings, memory is allocated dynamically. More memory can be allocated at run time on demand. As no memory is preallocated , no memory is wasted . Strings are slower when compared to implementation than character array #include < iostream > #include <string> using namespace std ; int main() { string str ; getline ( cin , str ); // cin >> str ; cout << str << endl ; return 0; }

16. Strings class functions in C++ insert() function: This function inserts a string at a specified location in the called string. append() function: This method appends one string at the end of another string. erase() function: This function erases a single or multiple character starting at a specified location within the called string. #include< iostream > using namespace std ; int main() { string str ("Hello"); str.insert (2, " rr "); cout <<"String after Insert : " << str << endl ; string str1("Hello"); string str2("Hi"); str1.append(str2, 0, 10); cout <<"String after append : " << str1<< endl ; string str3="Welcome"; str3.erase(3,2); cout <<"String after erase : " << str3; }

17. Strings class functions in C ++ length() function: This method gives us the total length of a string. replace() function: This function replaces part of a string with another string. at() function: This method gives us a character present at a particular index in a string. #include< iostream > using namespace std ; int main() { string str ("Hello"); cout <<"String length : " << str.length ()<< endl ; string str1("Hello"); string str2("test"); str1.replace(2,2,str2); cout <<"String after replace : " << str1<< endl ; string str3="Welcome"; cout <<"Particular char in string : " << str3.at(3); } Output: String length : 5 String after replace : Hetesto Particular char in string : c

18. Strings class functions in C ++ swap() function: This method swaps one string with the content of another string. find() function: This method finds the given string start index. substr () function: This method finds and returns part of a string i.e. substring. #include< iostream > using namespace std ; int main() { string str ("Hello"); cout <<"Find given string index : " << str.find (" ll ")<< endl ; string str1("Hello"); string str2("test"); str1.swap(str2); cout <<"String after swaping : " << str1<<" "<<str2<< endl ; string str3="Welcome"; cout <<"substring of string : " << str3.substr(1,5); } Output: Find given string index : 2 String after swaping : test Hello substring of string : elcom

19. Strings class functions in C ++ capacity() function: This method returns the total number of elements that can be stored in a string. empty() function: The  empty()  function returns 1 if string is empty and 0 if it is not empty. push_back () function: This method is used to push (add) characters at the end (back) of a string . pop_back () function: This method is used to pop (remove) 1 character from the end (back) of a string. #include< iostream > using namespace std ; int main() { string str ; cout <<"Find empty string : " << str.empty ()<< endl ; cout <<"Find capacity of string : "<< str.capacity ()<< endl ; str ="Find capacity of string"; cout <<"Find capacity of string : "<< str.capacity ()<< endl ; string str1="Welcome"; str1.push_back('a'); cout <<" push_back of string : " <<str1 ; str1.pop_back(); cout <<"string after pop_back : " << str1 ; } Output: Find empty string : 1 Find capacity of string : 15 Find capacity of string : 30 push_back of string : Welcomea string after pop_back : Welcome

20. Strings class functions in C ++ resize () function: The resize() function is used to either increase or decrease the size of a string . String copy, concatenation, compare #include< iostream > using namespace std ; int main() { string str1="First"; string str2="Second"; string str3,str4; //string copy str3=str1; cout <<"copy str1 ro str3:"<<str3<< endl ; //string concatenation str4=str3+str2; cout <<" concat str3 ro str2:"<<str4<< endl ; //string compare if(str1==str2) { cout <<"str1 and str2 are equal"; } else { cout <<"str1 and str2 are not equal"; } } Output: copy str1 ro str3:First concat str3 ro str2:FirstSecond str1 and str2 are not equal

21. Strings class functions in C ++ String Iterator in C++: Iterators are used for traversing or accessing all the characters of a string. Iterator functions are begin() function and this gives the beginning index of this string end() This gives the ending index of a string . ‘ rbegin ()’ and ‘ rend ()’ is reverse begin and reverse end. #include < iostream > #include < string.h > using namespace std ; int main () { string str = "Hello"; string:: iterator it; for ( it = str.begin () ; it != str.end () ; it++ ) { cout << *it; } cout << endl ; return 0; } Output: Hello #include < iostream > using namespace std ; int main() { string str = "Hello"; string:: reverse_iterator it; for (it = str.rbegin (); it != str.rend (); it++) { cout << *it; } } Output : olleH

22. Strings class functions in C ++ BASIS FOR COMPARISON CHARACTER ARRAY STRING Basic Character array is collection of variables, of character data type. String is class and variables of string are the object of class "string". Syntax char array_name [size]; string string_name; Indexing An individual character in a character array can be accessed by its index in array. In string the particular character can be accessed by the function string_name.at(index) / string_name [index] Size Static Dynamic Operators Operators in C++ can not be applied on character array. You may apply standard C++ operator on the string. Boundary Array boundaries are easily overrun. Boundaries will not overrun. Access Fast accessing. Slow accessing.